1. Field
Embodiments of the present invention are generally directed to measuring optical spectra of other properties of airborne particles that can be used for detection or characterization of particles in air, including harmful biological and chemical particles in air.
2. Description of Related Art
Airborne particles pose many problems. They can impact human health, agriculture, and the earth's climate. Pollens and fungal spores can cause allergies such as hay fever. Asthma can be exacerbated by airborne particles such as pollens and pollen fragments, particles from fungi, including fungal spores, bacteria, proteins from cats and dogs, and particles from cockroaches, and dust mites. Airborne particles, primarily bacteria and viruses, but also some fungi, are a primary means of disease transmission in humans and other animals. Fungal spores and bacteria transmit diseases of agricultural crops that are responsible for tremendous losses each year.
Primary Biological Aerosol Particles (PBAP) include bacteria, fungi, pollens, viruses, algae, protein allergens from cats and other animals, bits of leaves, plants, skin, dandruff, etc. These particles may be aerosolized by airflows, abrasion, and by injection (e.g., sneezing by animals or expulsion of spores by fungi). In addition to these commonly-identified particles, the PBAP may also include fragments of those particles, e.g., micron-sized particles that form when pollen grains undergo osmotic shock and rupture within the anthers or catkins of anemophilous plants may later be released into the air to form a respirable, antigen laden aerosol. Similarly, allergen-laden fungal fragments can be much smaller than the fungal spores. PBAP also includes re-aerosolized materials. Plants, fungi, and some animals have evolved efficient mechanisms to inject their pollens, spores, or their offspring, etc., into the air.
There are large differences in the estimates of both PBAP emissions into the atmosphere and atmospheric loadings. PBAP has been reported to contribute as much as 25% of the total mass of atmospheric particulate matter. Fluorescent biological aerosol particles were found to contribute 28% of the total particle number (in the 0.8-20-mm diameter range) above a forest canopy in Borneo, Indonesia. The global average concentration of fungal spores has been estimated to be approximately 1 mg/m3. There are large differences in estimates of total PBAP emissions.
FIG. 1 is a schematic illustration of some sources of atmospheric aerosols and their chemical and photochemical transformations. An atmospheric aerosol 10 can be extremely complex. Biological particles found in the atmosphere may include organisms such as bacteria, fungal spores, viruses, pollens, fragments of plants, fungi, etc. Complex mixtures can occur in particles because of (a) emission of complex particles, (b) adsorption of gasses by particles, (c) agglomeration of particles, (d) chemical and photochemical reactions of particles, and (e) cycling of particles through clouds. Sunlight provides the energy necessary for many chemical reactions in particles. Long range transport occurs over thousands of miles, such as for example, from China to California and from the Sahara Desert to the Carolinas.
Many particles in the atmosphere are complex mixtures. These result from emissions of complex particles, and adsorption, agglomeration, chemical reactions which can occur, especially in cycling though clouds. Sunlight provides the energy for many atmospheric chemical reactions affecting particle composition. Bacteria, pollens and other PBAP can also act as cloud condensation nuclei, and thereby affect rain deposition patterns, cloud coverage, and global climate. Also, many PBAP, including many pollen and fungal particles, and other carbon-containing aerosols (e.g., soot) absorb atmospheric radiation and re-emit some of that radiation at ultraviolet and visible wavelengths. Therefore, the absorption and fluorescence properties of atmospheric pollen and fungal materials are relevant for understanding their effects on climate. Some of the, if not the, largest uncertainties in global climate models are attributable to the uncertainties regarding the effects of aerosols. Some aerosols (e.g., soot) can contribute to warming by absorbing light. Other aerosols (composed of, e.g., bacteria, silica dust, or ammonium sulfate) can contribute to cooling by scattering light or by acting as cloud condensation nuclei which help generate cloud droplets which also scatter light, preventing sunlight from reaching the earth.
Optical trapping and manipulation of micron-sized particles, nanoparticles, molecules, and atoms have been used in aerosol science, chemistry, physics, biology, and interdisciplinary studies. For example, in one type of radiation pressure trap, commonly referred to as optical tweezers, a tightly-focused beam is used to hold particles. Other optical trapping methods have also been reported, e.g., using longitudinal trapping, holographic methods, self-reconstructing beams, and axicon(s). Combinations of trapping with other analytical techniques, e.g., Raman spectroscopy of particles in air or in liquid, provide ways to analyze molecular composition and to study time-varying phenomena, e.g., dynamic reactions in individual living cells.
Methods and devices exist for counting and characterizing airborne pollens, fungal and plant spores, bacteria, protein allergens, and other PBAP.
These techniques, however, are not without drawbacks. For example, airborne biological agents, such as anthrax or plague, can be dispersed at such low concentrations that no one would suspect a release until after persons got sick and went to the doctor. Although, forecasts related to allergens are available in much of the world, counting and classifying pollens to the genus or species level is presently performed by labor-intensive microscopic analysis of collected samples. At present, it is prohibitively expensive to measure bacteria, protein toxins or allergens, pollen and fungal spores with sufficient spatial and temporal resolution and specificity to provide adequate warning of a bioagent attack, or to provide adequate forecasts for persons with allergies. The times required for sampling and analyzing airborne bacteria, pollen and fungal particles preclude real-time alerts of hazardous conditions, and they make more difficult potential studies of the effects of bacteria, pollens or fungal particles on atmospheric processes, or studies of transmission of fungal diseases of plants.
Improved, automated, and near-real-time techniques for characterizing bacteria, pollens, fungal spores, and other PBAP may be useful.